Compounds of the present invention can be characterized as pentaerythritol cyclic diphosphates and diphosphoramidates. The diphosphates are further characterized by halogen substitution on the oxyaliphatic or oxyalicyclic groups of the ester moiety. The diphosphoramidates can be optionally substituted with halogen atoms on the hydrocarbon substituents attached to the nitrogen atoms.
During the past several years, a large number of flame-retardants have been developed for use with an almost equally large number of flammable materials. Cellulosic materials such as paper and wood and polymeric materials such as synthetic fibers and bulkier plastic articles are just two examples of materials for which flame retardants have been developed. For any class of flammable materials, such as synthetic high polymers, those skilled in the art have long been aware that some flame-retardant additives are more effective in some polymers than they are in others. In fact, many flame-retardant additives which are highly effective in some polymer systems are virtually ineffective in other polymer systems. The mere fact, therefore, that most flame-retardants contain halogen and phosphorus atoms does not assure that any given halogenated or phosphorus-containing compound will impart useful flame-retardant characteristics to all or even to any polymeric systems. Furthermore, as those skilled in the art have improved the flame-retardancy of many polymeric materials, they have been simultaneously required to provide the necessary flame retardancy with a minimal effect upon other properties of the polymers such as their light stability, moldability and flexural, tensile and impact strengths. Balancing all of the foregoing considerations and thereby developing polymeric compositions with good flame-retardant characteristics as well as a satisfactory balance of other properties is, consequently, a task which has in the past and presently continues to require the exercise of a high degree of inventive skill.